1. Technical Field
The present invention relates to a projection apparatus and an image display apparatus.
2. Related Art
As the development of projectors proceeds in recent years, there is a need for a projector that projects an image on a predetermined projection surface (a screen, for example) in the diagonally upward, downward, rightward, or leftward direction. As a method for diagonally projecting an image on a screen, it is conceivable to employ a configuration in which the optical axis of a projection lens is inclined to the central axis of incident light, a configuration in which a decentered focusing lens is used to deflect the light emitted from a light source toward a screen (see JP-A-11-327047, for example), and a configuration, as shown in FIG. 5, in which the optical axis O1 of a front lens group 201 is shifted from the central axis O3 of incident light.
In the projection apparatus described in JP-A-11-327047, the light emitted from a light source is incident on a cylindrical lens, and the light having exited from the cylindrical lens is collected by a collector lens. The collected light is focused by a decentered focusing lens in the area above the central axis of the light emitted from the light source, and projected by a projection lens. Using the decentered focusing lens to deflect the central axis of the light as described above allows an image to be diagonally projected without tilting the entire projection apparatus.
In the configuration shown in FIG. 5, the optical axis O1 of a front lens group 201 and the optical axis O2 of a rear lens group 202 are shifted from each other but parallel to each other, and the front lens group 201 is disposed in such a way that the central axis O3 of incident light is located, for example, below the optical axis O1 of the front lens group 201 in the plane of view. Therefore, the light incident from the area below the optical axis O1 of the front lens group 201 exits from the front lens group 201, and enters the area above the optical axis O2 of the rear lens group 202. The light having passed through the rear lens group 202 is projected toward the portion of a projected surface that is above the central axis O3, where the light was incident on the front lens group 201.
However, as described above, in the configuration in which a projection lens is inclined, the configuration described in JP-A-11-327047, and the configuration in which the front lens group and the rear lens group are disposed in such a way that the optical axes thereof are shifted from each other, the apparatus becomes thicker in the direction in which the projection lens is inclined, in the direction in which the optical axis is deflected, and in the direction in which the optical axes of the front lens group and the rear lens group are shifted, respectively. The overall apparatus thus disadvantageously becomes larger.